The 2003 Northeast Blackout
On 14 August 2003, Midwest and Northeast United States, and Ontario: A control room alarm failure and a line brushing overgrown trees in Ohio cascaded into the largest blackout in North American history.
Key Facts
- The blackout began just after 4pm Eastern time on 14 August 2003.
- About 50 million people across 8 US states and Ontario lost power.
- Some areas were without power for up to 4 days.
- It led to mandatory reliability standards for the North American grid.
What Happened
On the afternoon of 14 August 2003, an overloaded transmission line sagged into trees near Cleveland, Ohio, and tripped offline. A software fault meant the alarm that should have alerted operators at FirstEnergy never sounded, so the fault went unaddressed as more lines overloaded and failed in turn.
Within about an hour the cascade had spread across the interconnected grid, cutting power to an estimated 50 million people across eight US states and the Canadian province of Ontario. Some areas of the United States were without power for up to four days, and parts of Ontario faced rolling blackouts for more than a week.
The joint US-Canada task force that investigated the blackout put total costs in the United States at between 4 and 10 billion US dollars, and its recommendations led to mandatory, enforceable reliability standards for the North American grid where before they had been voluntary.
Cause
Cascading failure after an alarm system fault and a line contacting trees
Researched independently from public reporting, not from this site's own data. Source: US Department of Energy.